Glass fibre reinforced polycarbonate composition met improved toughness

ABSTRACT

The invention relates to a polycarbonate composition containing: a) 40-69.5 mass % of aromatic polycarbonate having a limiting viscosity number of 43-52 ml/g, b) 30-50 mass % of sized glass fibres, c) 0.5-5 mass % of at least one partially hydrogenated block copolymer containing at least two terminal polymer blocks A of a monoalkenylarene and at least one intermediate polymer block B of a conjugated diene, and optionally d) 0-25 mass % of other additives, and where the sum of a-d) is 100 %. The composition combines improved toughness, for example increased elongation at break and improved environmental stress cracking resistance, and high strength and rigidity. The invention also relates to a process for producing the polycarbonate composition according to the invention, to a moulded part that contains this composition and to an article that contains such a moulded part.

The invention relates to a glass fibre reinforced and elastomer-modifiedpolycarbonate composition. The invention also relates to a process forproducing a polycarbonate composition according to the invention, to amoulded part containing this composition and to an article containingsuch moulded part.

Such a polycarbonate composition is known from for example patentapplication DE 3926904 A1. That publication describes a polycarbonatecomposition containing 30 to 93 mass % of polycarbonate, 5 to 50 mass %of glass fibres and 2 to 20 mass % of at least one elastomer. Thiscomposition preferably contains as elastomer 6 to 15 mass % of an ABS,that is, a graft copolymer of at least styrene and acrylonitrile on arubber-like polymer of at least butadiene, optionally mixed with acopolymer of at least styrene and acrylonitrile.

A glass fibre reinforced polycarbonate composition containing relativelylarge amounts of glass fibres, for example 30 to 50 mass %, exhibitshigh rigidity, strength and dimensional stability and can be applied formaking parts that can replace metal parts. Such a composition often alsoshould show good toughness, in particular an object obtained from such acomposition should exhibit sufficient elongation at break in order to beable to withstand for example deformation arising as a screw is drivenin, without crack and/or craze formation. Although polycarbonate isknown to be a highly tough material, a glass fibre reinforcedpolycarbonate composition containing more than 10 mass % of glass fibresrather tends to exhibit a brittle character. The toughness of a polymercomposition can in many cases be increased by adding an amount of atoughness-improving, or impact-modifying, elastomer.

A drawback of the known polycarbonate composition according to DE3926904 A1 is that it does not show the desired toughness, especiallywhen it contains relatively large amounts of glass fibres, that is from30 to 50 mass %. Therefore, the object of the invention is to providesuch a glass fibre reinforced and elastomer-modified polycarbonatecomposition that does not show said drawback or shows it at least to alesser extent.

This object is achieved according to the invention with a polycarbonatecomposition that contains the following components:

-   -   a) 40-69.5 mass % of aromatic polycarbonate having a limiting        viscosity number of 43-52 ml/g; as measured on a solution of        polycarbonate in dichloromethane according to ISO 1628/4,    -   b) 30-50 mass % of sized glass fibres,    -   c) 0.5-5 mass % of at least one partially hydrogenated block        copolymer containing at least two terminal polymer blocks A of a        monoalkenylarene and at least one intermediate polymer block B        of a conjugated diene, and optionally    -   d) 0-25 mass % of other additives,        and wherein the sum of a)-d) is 100%.

The polycarbonate composition according to the invention exhibits hightoughness, as manifested in for example increased elongation at break ina tensile test. Another advantage is that the composition also has agood colour and colour stability. A further advantage of thepolycarbonate composition according to the invention is that it containsa relatively small amount of elastomer, as a result of which thecomposition exhibits high strength and rigidity. A further advantage ofthe invention is that the composition exhibits relatively low meltviscosity so that thin-walled objects, too, can be produced from itwithout problems. Yet another advantage is that the polycarbonatecomposition according to the invention exhibits improved resistance tocrack formation as initiated by certain chemicals (improved ESCR, orenvironmental stress cracking resistance).

It is known from GB 2004284 A, DE 2839356 A1 and U.S. Pat No. 4,537,930that adding a quantity of said partially hydrogenated block copolymer toa polycarbonate can improve a number of properties, but thesepublications focus on unreinforced compositions, or compositionscontaining not more than 5 mass % of glass fibres. Said publications donot describe that this measure will also be effective for increasing thetoughness of compositions that contain 30 to 50 mass % of glass fibre,which compositions are known to have a different failure mechanism thanunreinforced polycarbonate. In EP 0053825 A1 it is taught that in orderto improve toughness of reinforced polycarbonate compositions unsizedfibrous reinforcing agents should be applied, and optionally up to 10mass % of said block copolymer. It is further stated that said blockcopolymer has a detrimental effect on stiffness, and results in only aminor improvement in impact strength, in any event, if applied in acomposition containing sized reinforcing fibres.

The polycarbonate composition according to the invention contains interalia 40-69.5 mass % of aromatic polycarbonate of specified viscosity.Suitable aromatic polycarbonates are polycarbonates made from at least adivalent phenol and a carbonate precursor, for example by means of aninterfacial polymerization process. Suitable divalent phenols that maybe applied are compounds having one or more aromatic rings that containtwo hydroxy groups, each of which is directly linked to a carbon atomforming part of an aromatic ring. Examples of such compounds are4,4′-dihydroxybiphenyl, 2,2-bis(4hydroxyphenyl)propane (bisphenol A),2,2-bis(4-hydroxy-3-methylphenyl)propane,2,2-bis-(3-chloro-4-hydroxyphenyl)-propane,2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane,2,4-bis-(4-hydroxyphenyl)-2-methylbutane,2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane,4,4-bis(4-hydroxyphenyl)heptane,bis-(3,5-dimethyl-4-hydroxyphenyl)-methane,1,1-bis-(4-hydroxyphenyl)-cyclohexane,1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-cyclohexane,2,2-(3,5,3′,5′-tetrachloro-4,4′-dihydroxydiphenyl)propane,2,2-(3,5,3′,5′-tetrabromo-4,4′-dihydroxydiphenyl)propane,(3,3′-dichloro-4,4′-dihydroxyphenyl)methane,bis-(3,5-dimethyl-4-hydroxyphenyl)-sulphon, bis-4-hydroxyphenylsulphon,bis-4-hydroxyphenylsulphide.

The carbonate precursor may be a carbonyl halogenide, a halogen formateor carbonate ester. Examples of carbonyl halogenides are carbonylchloride and carbonyl bromide. Examples of suitable halogen formates arebis-halogen formates of divalent phenols such as hydroquinone or ofglycols such as ethylene glycol. Examples of suitable carbonate estersare diphenyl carbonate, di(chlorophenyl)carbonate,di(bromophenyl)carbonate, di(alkylphenyl)carbonate, phenyltolylcarbonateand the like and mixtures thereof. Although other carbonate precursorsmay also be used, it is preferred to use the carbonyl halogenides and inparticular carbonyl chloride, also known as phosgene.

The aromatic polycarbonates in the composition according to theinvention may be prepared using a catalyst, an acid acceptor and acompound for controlling the molecular mass.

Examples of catalysts are tertiary amines such as triethylamine,tripropylamine and N,N-dimethylaniline, quaternary ammonium compoundssuch as tetraethylammoniumbromide and quaternary phosphonium compoundssuch as methyltriphenylfosfoniumbromide.

Examples of organic acid acceptors are pyridine, triethylamine,dimethylaniline and so forth. Examples of inorganic acid acceptors arehydroxides, carbonates, bicarbonates and phosphates of an alkali metalor earth alkali metal.

Examples of compounds for controlling the molecular mass are monovalentphenols such as phenol, p-alkylphenols and para-bromophenol andsecondary amines.

Such polycarbonates, their preparation and properties are described indetail in for example Encycl. Polym. Sci. Eng., 11, p. 648-718 (Wiley,New York, 1988) and in Kunststoff Handbuch, 3/1, p. 117-297 (HanserVerlag, Muenchen, 1992).

The composition according to the invention contains a polycarbonatehaving a limiting viscosity number (LVN) of 43-52 ml/g as measured indichloromethane. A polycarbonate of lower viscosity results in too lowtoughness of the composition, whereas a higher viscosity has a negativeeffect on dispersability of glass fibres and melt flow of thecomposition. Therefore, the polycarbonate applied in the compositionpreferably has a limiting viscosity number of 44-50, more preferably45-48 ml/g.

The composition according to the invention preferably contains apolycarbonate derived from bisphenol A and phosgene and optionally minoramounts of other compounds having one, two or more than two reactivegroups as comonomers, for instance for controlling the melt viscosity.

The polycarbonate composition according to the invention contains amongother things 30-50 mass % of sized glass fibres. Suitable glass fibresnormally have a diameter of 5 to 25 microns, preferably 7 to 15 microns.Sized glass fibres is understood to mean that the fibres have beenprovided with a coating or sizing, which is designed to improve bothprocessability and adhesion to polycarbonate. Such glass fibres withsizing optimised for use in polycarbonate are commercially available.Glass fibres may be added to the composition according to the inventionin the form of cut fibres a few millimetres long (also known as choppedstrands). However, the composition may also contain glass fibres thatare supplied to an extruder in the form of continuous fibres(‘rovings’). The polycarbonate composition preferably contains choppedstrands. The average length of the glass fibres in the compositionaccording to the invention may vary between wide limits, but the averagelength preferably is about 0.1 to 0.5 mm. The advantage of a largerlength is a higher strength of the composition, while shorter fibresenhance the processability of the composition. A further advantage isthat articles made from them have a more isotropic character.

The polycarbonate composition according to the invention furthercontains 0.5-5 mass % of at least one partially hydrogenatedhydrogenated block copolymer containing at least two terminal polymerblocks A of a monoalkenylarene and at least one intermediate polymerblock B of a conjugated diene. Suitable partially hydrogenated blockcopolymers contain at least two terminal polymer blocks A of amonoalkenylarene having an average molecular mass of 5,000-125,000 andat least one intermediate polymer block B of a conjugated diene havingan average molecular mass of 10000-300000 g/mol, with the terminalpolymer blocks A accounting for 8-55 mass % of the block copolymer andwith not more than 25% of the aromatic double bonds of the polymerblocks A and at least 80% of the aliphatic double bonds of the polymerblocks B being reduced through hydrogenation. If the monoalkenylarene insuch block copolymers is styrene, they are also referred to asstyrene/ethene-co-butene/styrene block copolymers, or SEBS for short.Such SEBS block copolymers may further contain a functional group forincreasing polarity or for attaining reactivity with other polymers. Thepolycarbonate composition may also contain a mixture of different typesof block copolymers, for example of different molecular masses, or amixture of block copolymers that either have or do not have a functionalgroup. Useful block copolymers for the compositions according to theinvention are described in patent specification NL 183467 A and arecommercially available under trade names such as Kraton™ G1650, G1651,G1652, G1657, G1726 and G1855 (Kraton Polymers, BE).

The composition according to the invention preferably contains 35 to 45mass % of sized glass fibres. At such high glass fibre concentrationsthe advantages of the invention are most manifest, and a desiredcombination of strength, rigidity and toughness is obtained. In aparticular embodiment according to the invention the compositioncontains 38-42, or about 40 mass % of glass fibres.

In a further preferred embodiment the composition according to theinvention contains between 1 and 3 mass % of block copolymer, morepreferably 0.75-4, or 1.5-2.5 mass %. Such a composition exhibits goodtoughness while retaining strength and rigidity, good flowability andimproved ESCR. The composition according to the invention mostpreferably contains about 2 mass % of block copolymer, because thatcomposition exhibits an optimum combination of properties.

The polycarbonate composition according to the invention may furthercontain from 0 to 25 mass % of one or more other additives. Theseinclude the customary additives such as stabilizers against thermal orthermo-oxidative degradation, stabilizers against hydrolyticdegradation, stabilizers against degradation from light, in particularUV light, and/or photo-oxidative degradation, processing aids such asrelease agents and lubricants, colorants such as pigments and dyes,fillers including minerals such as wollastonite or aluminium silicates,or flame retardants. Suitable examples of such additives and theircustomary amounts are stated in the aforementioned Kunststoff Handbuch,3/1.

Although a polycarbonate such as bisphenol-A polycarbonate in itself hasa fairly good flame retarding behaviour, a polycarbonate composition ispreferably rendered flame retardant by adding one or more flameretarding compounds. Suitable examples of flame retarding compounds arecertain alkali or earth alkali sulphonates, sulphonamide salts,perfluoroborates, halogenated compounds, especially bromated aromaticcompounds, and phosphorus-bearing organic compounds, especiallyphosphate esters such as triphenyl phosphate. Suitablephosphorus-bearing compounds are described in for example DE 19828535 A1(Komponente E), in EP 0640655 A2 (Komponente D) and in EP 0363608 A1(component C). As flame retarding compound use is preferably made of atleast an oligomer phosphate ester, such as resorcinol diphenylphosphate(RDP), bisphenol-A diphenylphosphate (BDP) or mixtures thereof. Suchcompositions exhibit an excellent combination of mechanical, flameretarding and processing properties. Additionally the composition oftencontains a fluoropolymer such as polytetrafluoroethylene to enhance itsdripping properties in a fire test.

The invention also relates to a process for making a glass fibrereinforced and elastomer modified polycarbonate composition according tothe invention.

Publication DE 3926904 A1 describes a process for making a polycarbonatecomposition containing 30 to 93 mass % of polycarbonate, 5 to 50 mass %of glass fibre and 2 to 20 mass % of at least one elastomer. It ispreferred to apply 6 to 15 mass % of an ABS as elastomer in thecomposition. DE 3926904 A1 teaches to produce these compositions by aprocess whereby first at least polycarbonate and glass fibres aremelt-mixed, with an elastomer subsequently being added. This processaims to reduce the temperature increase during melt-mixing, and thus toreduce degradation of the elastomer, so producing a glass fibrereinforced polycarbonate composition with improved toughness.

A drawback of the known process according to DE 3926904 A1 is that thetemperature increase during melt-mixing of polycarbonate and relativelylarge amounts of glass fibres, for example 30 to 50 mass %, is stillsuch that a composition having the desired toughness is not obtained. Afurther drawback of the said process is that the specified stagedaddition and mixing of components is troublesome to carry out inpractice and, moreover, results in more breakage of glass fibresparticularly in the case of relatively large amounts of glass fibres, asa result of which the strength of the composition diminishes.

The object of the invention therefore is to provide a process forproducing a glass fibre reinforced and elastomer-modified polycarbonatecomposition that does not have the said drawbacks or has those drawbacksto a lesser extent.

This object is achieved according to the invention by a process wherebythe components as defined in Claim 1 are melt-mixed.

By the process according to the invention there is obtained apolycarbonate composition that exhibits a desired combination ofrigidity, strength and toughness, the order in which the components areadded not being critical and with a smaller temperature increase arisingduring melt-processing. Consequently the composition also has animproved colour and colour stability. A further advantage is thatchopped glass fibres can be added to a molten mixture containing atleast polycarbonate and block copolymer with the aid of a mixingextruder such as a twin-screw extruder. This presents the advantage thatglass fibres are well dispersed and are not subject to serious breakage,whilst the melt temperature does not rise too far.

The process according to the invention can be carried out using mixingdevices customary for producing a polymer composition by melt-mixing thecomponents. Suitable mixing devices are single-screw or twin-screwextruders, preferably twin-screw extruders having a feeding system tothe melt, in particular for feeding glass fibres. In general, thecomponents are fed to the extruder in dry form, optionally pre-mixed,and then melt-mixed, whereupon the mixture obtained is extruded intostrands and chopped into granules. The melt temperature may increase towell above 300° C. because of the high viscosity and high shear forces.However, it is preferred for the melt temperature during mixing not toincrease to more than 350° C., in particular not to more than 340° C.

The invention also relates to moulded parts that contain thepolycarbonate composition according to the invention. The inventionrelates in particular to a moulded part produced by injection mouldingof the composition according to the invention. Advantages of such amoulded part are good mechanical properties, in particular high strengthand rigidity, and good toughness, in particular improved resistance tocrack formation as initiated by certain chemicals such as organicsolvents (i.e. good environmental stress cracking resistance or ESCR).Such moulded parts may replace for example metal moulded parts, withespecially lower weight and greater design freedom being advantageous.This is especially advantageous for moulded parts that are a structuralelement of a small but complex appliance such as a mobile telephone(GSM), a personal digital assistant (PDA), and the like. The improvedtoughness allows higher loading of screwed joints or ‘snap fit’ jointsbetween moulded parts.

The invention accordingly also relates to an article that contains amoulded part produced from the composition according to the invention.

The invention will now be elucidated with reference to the followingexamples and comparative experiments.

Materials

Polycarbonate: use was made of bisphenol A polycarbonates with alimiting viscosity number of about 48, 45 and 41 ml/g, indicated aspolycarbonate A, B, and C, respectively;

Glass fibres: standard glass fibres with a diameter of 14 microns,chopped length 4 mm and with a sizing suitable for polycarbonate;

Block copolymer: an SEBS, type Kraton™ G1650 (Kraton Polymers, BE);

ABS: a mixture of Ronfalin® FZ311 and Ronfalin® FZ330 in the ratio of10/6.5 (DSM, NL).

Determination of properties

LVN: the limiting viscosity number was measured on a solution ofpolycarbonate in dichloromethane according to ISO 1628/4;

MFI: the melt flow index was determined at 300° C. and a load of 1.2 kgaccording to ISO 1133;

Tensile strength and elongation at break were determined according toISO 527-1 using a standard test bar injection-moulded to Campusguidelines;

Impact strength: the impact strength of a standard test bar was measuredaccording to the Izod reversed notched method (ISO 180-4AR);

ESCR: the environmental stress cracking resistance was determined bymeasuring a test bar's elongation at break after 30 minutes' exposure toa 1/3 toluene/propanol mixture and application of a particularpre-strain using a jig (ASTM 638/M3);

Screw test: the resistance to crack and/or craze formation fromdeformation and the presence of chemicals was determined on aninjection-moulded object made from the composition and having a hollow,cylindrical projection with outside and inside diameters of 4.1 and 2.0mm, respectively. A cylindrical screw of outside diameter 2.35 mm wasdriven into the hollow cylinder with a force of 0.4 Nm using a torquescrew driver. Next, the object with the screw was submerged in a 1/3toluene/propanol mixture for 30 seconds. Crack formation, if any, wasobserved visually.

EXAMPLE 1 and Comparative Experiments A-C

The components stated in Table 1 plus a stabilizer combinationconsisting of 0.05 mass % of a phosphite compound (Irgafos 168) and 0.2mass % of a hindered phenol compound (Irganox 1076), 0.4 mass % releaseagent (Loxiol EP861) and a mixture of colouring agents consistingessentially of about 1.5 mass % of TiO₂ were mixed in a W&P ZSK40twin-screw extruder at a speed of 350 rpm and temperature setting of260-280° C., by feeding polycarbonate, elastomer and additives to thethroat and adding glass fibres to the melt using a side feeder. In thecase of the compositions that contained SEBS a lower melt temperaturewas observed, with the extruder throughput and torque being higher andlower, respectively (in particular Example 1 versus Comp. Exp. A).

The dark grey granules thus obtained were then injection-moulded intotest bars at a temperature setting of 280-290° C.

Example 1 exhibits distinctly better toughness, higher elongation atbreak and higher impact strength than the composition without elastomer,whilst the presence of ABS does result in lower tensile strength but notin improved toughness. In addition, the injection-moulded products thatcontain ABS exhibit somewhat lower rigidity (tensile modulus).

EXAMPLE 2 and Comparative Experiments D-F

The compositions stated in Table 2 were made analogously to Example 1and comparative experiments A-C except that the extruder speed washigher. The compositions also contained the aforementioned additives. Asa result, the melt temperature observed for Comp. Exp. A increased to350° C., while addition of only 2 mass % of SEBS resulted in asignificant temperature decrease, also when ABS was also present.

Injection-moulded products according to Example 2 again exhibited highertoughness than compositions D-F, with the tensile strength also beinghigher than for E and F. The ESCR tests, too, revealed higher toughnessand resistance to organic solvents.

In a screw test, only Example 2 did not show any damage afterdeformation by driving in a screw and exposure to a mixture of solvents.

EXAMPLES 3-4 and Comparative Experiment G

The compositions stated in Table 3 were made analogously to Example 1.Example 3 indicates that toughness improvement is also observed for aslightly increased glass fibre content. If the viscosity of thepolycarbonate is somewhat decreased an even better balance of propertiesis observed (Ex. 4). Further decreasing the viscosity of polycarbonateresults in a drop of properties. Apparently there is an optimum range ofpolycarbonate viscosity for the present elastomer-modified compositionscontaining high amounts of glass fibres. TABLE 1 Comp. Comp. Comp.Example 1 Exp. A Exp. B Exp. C Composition unit Polycarbonate A Parts by58 60 43.5 41.5 Glass fibre mass 40 40 40 40 Block copolymer 2 0 0 2 ABS0 0 16.5 16.5 Mixing at 350 rpm Throughput kg/hour 139 122 138 140Torque % 80 85 76 76 Melt temperature ° C. 336 345 327 312 PropertiesMFI (300° C./1.2 kg) dg/min 10.7 10.5 6.7 6.3 Tensile strength MPa 93 9080 81 Elongation at break % 1.8 1.4 1.2 1.3 Impact resistance kJ/m² 2423 15 16

TABLE 2 Comp. Comp. Comp. Example 2 Exp. D Exp. E Exp. F Compositionunit Polycarbonate A Parts by 58 60 43.5 41.5 Glass fibre mass 40 40 4040 Block copolymer 2 0 0 2 ABS 0 0 16.5 16.5 Mixing at 417 rpmThroughput kg/hour 140 140 142 140 Torque % 75 82 78 72 Melt temperature° C. 326 350 325 315 Properties MFI (300° C./1.2 kg) dg/min 9.5 10.7 7.06.4 Tensile strength MPa 95 98 80 80 Elongation at break % 1.8 1.5 1.21.3 Impact resistance kJ/m² 29 26 14 15 ESCR; elongation at break   0%pre-strain % 1.9 1.4 1.2 1.3 0.5% pre-strain % 1.8 1.4 1.2 1.3 0.8%pre-strain % 1.8 1.7 1.2 1.2 Screw test no cracks cracks cracks cracks

TABLE 3 Comp. unit Example 3 Example 4 Exp. G Composition PolycarbonateA Parts by 56 Polycarbonate B mass 56 Polycarbonate C 56 Glass fibre 4242 42 Block copolymer 2 2 2 Properties MFI (300° C./1.2 kg) dg/min 10.216.0 26.5 Tensile strength MPa 95 96 85 Elongation at break % 1.8 1.81.4 Impact resistance kJ/m² 24 26 14 Screw test No cracks No crackscracks

1. Glass fibre reinforced and elastomer-modified polycarbonatecomposition that contains the following components: a) 40-69.5 mass % ofaromatic polycarbonate having a limiting viscosity number of 43-52 ml/g; as measured on a solution of polycarbonate in dichloromethaneaccording to ISO 1628/4, b) 30-50 mass % of sized glass fibres, c) 0.5-5mass % of at least one partially hydrogenated block copolymer containingat least two terminal polymer blocks A of a monoalkenylarene and atleast one intermediate polymer block B of a conjugated diene, andoptionally d) 0-25 mass % of other additives, wherein the sum of a)-d)is 100%.
 2. Polycarbonate composition according to claim 1, wherein thepolycarbonate is derived from bisphenol A and phosgene.
 3. Polycarbonatecomposition according to claim 1, wherein the glass fibres have anaverage length of 0.1 to 0.5 mm.
 4. Polycarbonate composition accordingto claim 1, wherein the block copolymer is astyrene/ethene-co-butene/styrene block copolymer (SEBS). 5.Polycarbonate composition according to claim 1 that contains 35-45 mass% of glass fibres.
 6. Polycarbonate composition according to claim 1,that contains 1-3 mass % of block copolymer.
 7. Process for making aglass fibre reinforced and elastomer-modified polycarbonate compositionaccording to any claim 1, wherein the various components are melt-mixed.8. Process according to claim 7 wherein chopped glass fibres are addedto a molten mixture containing at least polycarbonate and blockcopolymer.
 9. Moulded part that contains the polycarbonate compositionaccording to claim
 1. 10. Moulded part produced by injection moulding ofthe polycarbonate composition according to claim
 1. 11. Article thatcontains at least a moulded part according to claim
 9. 12. Polycarbonatecomposition according to claim 2, wherein the glass fibres have anaverage length of 0.1 to 0.5 mm.
 13. Article that contains at least amoulded part according to claim 10.